Contraceptive acceptance and pregnancy: a matrix approach to the analysis of competing risks

Abstract This paper represents an initial attempt to formalize the relationships among post-partum sterility, fecundability, and contraceptive acceptance in terms of absorbing Markov chains. Acceptance of contraception offered by family planning programmes is analyzed as a possible event in time for a cohort of recently delivered women as they pass through phases of temporary sterility and fecundability towards another possible pregnancy. The results of the study indicate that once a woman leaves the post-partum anovulatory stage, the probability of her becoming pregnant again is large compared to the competing rates of contraceptive acceptance currently in force. Unless highly fecund non-contracepting women are approached by family planning programmes shortly after a pregnancy has been terminated (by childbirth or abortion), they will quickly become ineligible to accept either the pill or IUD because of once again being 'currently pregnant'.     

Postamenorrheic versus postpartum strategies of contraception

The postpartum strategy of inserting an intra-uterine device shortly after a birth essentially eliminates the risk of conceiving again before starting contraception but maximizes the overlap between wearing time and postpartum anovulation when protection is not needed. In contrast, the postamenorrheic strategy of delaying insertion until right after the woman’s first menses all but removes overlap with anovulation but allows a chance of conception before start of contraception because sometimes an ovulation precedes the first menstruation. In this paper some algebra is developed and utilized to see which of the two strategies delays the next conception longer. The postamenorrheic strategy is found to have a slight advantage over the postpartum approach for a wide range of fecundability levels, lengths of anovulation, and rates of continuation of IUD. However this slight advantage presupposes that insertions are taking place at the exact time prescribed. When a progressively larger factor of procrastination is introduced, the advantage rapidly passes from the postamenorrheic to the postpartum approach. An explanation for the differing sensitivity of the two insertion strategies with respect to procrastination is derived from the results of an earlier analysis.     

Timing and sequence of resuming ovulation and menstruation after childbirth

Abstract This report presents results from a prospective study of post-partum physiology conducted by the Obstetric Department of the Catholic University of Chile during 1965-68. The study was undertaken to gain more detailed knowledge than is currently available about the relationship between a woman's lactation experience and the return of her post-partum reproductive function. 200 mothers were successfully followed and information collected about their intervals from childbirth to first ovulation and to first bleeding day, together with a detailed history of breast feeding. In these histories, days of 'full breast feeding' (infant exclusively breast-fed) are distinguished from days of 'partial breast feeding' (infant given supplementary nutrition besides breast milk). Elaborate pains were taken to establish the date of first ovulation, four different techniques being used concurrently during a series of weekly contacts with each patient.     

The time-varying performance of the long-run demand for money in the United States

This article investigates the issues of the stability and predictability and interest-sensitivity of money demand over 1870–1997. Two different estimation methodologies are used - random coefficient (RC) modeling and vector error correction (VEC) modeling. The former procedure allows the profiles of the coefficients to be traced over time and relaxes several restrictions routinely imposed in applied work. The results indicate that different estimation methodologies using different data periods and frequencies yield estimates of some of the coefficients of the long-run demand for money that fall within a fairly narrow range. The results also suggest that specification errors have had an important influence on the time profile of the interest elasticity of money demand and that there is a tendency for the interest elasticity to decline in absolute value as interest rates decline.     

The contraceptive potential of early versus delayed insertion of the intrauterine device

One argument for a postpartum program of contraception is minimizing chances that the mother will conceive again before she can accept contraception. However early insertion increases the extent of overlap between retention of the device and anovulation when the woman is protected anyway while at the same time reducing the average span of wearing time coinciding with fecundable months when protection is needed. Thus it is not clear that early insertion yields the maximal postponement of next conception. Delaying insertion three or even six months might accomplish more. To investigate this matter, a model has been developed which incorporates the following factors: time of insertion, distribution of anovulatory length, natural fecundability and rates of effectiveness and continuation of IUD. It turns out that predicated upon the distribution of anovulatory length regarded as most realistic, the penalty of early insertion in terms of reduced postponement of next conception proves consistently small.